1. Field of the Invention
This invention pertains generally to near-field optical devices and methods, and more particularly to an optical emitter apparatus and method utilizing a conductive plane with a resonant aperture configured for near field localization. The invention may be used with edge emitting, corner emitting and surface emitting semiconductor lasers as well as other near field radiation sources.
2. Description of the Background Art
Near-field optical techniques require the use of radiation source apertures and distances on the order of generally less than the wavelength λ of the radiation source. Near field optical technologies offer high optical data storage densities, increased microscopic resolution, and other advantages. Near field technologies have utilized surface and edge emitting lasers, tapered optical fibers with metallized surfaces, and solid immersion lens techniques.
One class of semiconductor lasers which has appeared promising for near-field applications are vertical cavity, surface emitting lasers or VCSELs. These surface or top-emitting lasers generally have laser cavity or “post” with an active region surrounded by stacks of interleaved quarter wave semiconductor layers which define mirrors about the active region laser cavity. The active region can be in bulk form or have single or multiple quantum well, quantum wire and/or quantum dot structures therein. There are also p- and n-type conductive regions included on opposite sides of the active region, and the VCSEL can be turned on and off by varying the current through the p-n junction diode.
Top surface emitting GaAs, AlGaAs, AlGaInP, InGaAs, InGaAsP and InP VCSEL devices are relatively easy and inexpensive to manufacture, and generally can be produced via low-cost, high volume semiconductor IC fabrication methods using metal organic vapor phase epitaxy (MOVPE), liquid phase epitaxy (LPE) or molecular beam epitaxy (MBE) techniques. The laser cavity structures are typically deposited or grown vertically on a substrate and have an emission face defined by ion implantation, lateral oxidation, by polyimide or other dielectric, or free-standing post. The lateral oxidation and dielectric encapsulant techniques will generally provide for a lower effective refractive index in the region bounding the core of the laser structure, resulting in improved optical confinement relative to the ion implanted emission face. However, VCSEL devices of both types generally have been demonstrated with good reproducibility, uniformity and reliability.
Currently available VCSEL devices can be designed to effectively provide transverse and longitudinal mode laser light with a relatively high degree of intrinsic polarization. VCSELs also provide a radially symmetric Gaussian near-field with low divergence angle, which simplifies coupling to optics or fibers. An important drawback of VCSEL devices, however, is that they provide relatively low single mode optical power output compared to edge emitting lasers. The limitation on power output has limited the use of VCSEL devices in near-field technologies. Edge-emitting diode laser devices are known which provide higher optical power, but such devices are much more difficult and expensive to manufacture, and further require relatively large drive currents for operation.
For the purposes of near field optical recording, the total power requirement is modest and within the capability of the VCSEL device. However, the power density at the emission facet is greatly reduced relative to the edge emitter. Since in near field applications it is the power density which is operative, the conventional edge emitter is advantaged over the conventional VCSEL.
There is accordingly a need for a near field optical device which provides high optical power density, which provides good near field localization, and which can be embodied in vertical cavity surface emitting lasers, edge emitting lasers and other radiation sources. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.